Radio location system



J. E. HAWKIN$ 10 LOCATION SYS 3 Sheets-Sheet. 1

Filed NQV. 27, 1%

INVENTOR James E Hawkins J. E. HAWKINS ammo LOCATION SYSTEM 3 Sheets-Sheet 3 Filed Nov. 27, 1948 P. (Receiver 27) 6 2 r -9v .N e c e R 2 P y m m n m Time FIG. 4

Beam Trace Beam Trace Zone 8 Zone A Receiver 27) Receiver 26) (Receiver 26) Inventor James E. Hawkins Patented July '4, 195% RADIO LOCATION SYSTEM James E. Hawkins, Tulsa, Okla, assignor to Seismograph Service Corporation, Tulsa, Okla., a

corporation of Delaware Application November 27, 1948, Serial No. 62,367

44 Claims.

9, 1947, and assigned to the same assignee as the present application.

Aside from various types of radio direction finding systems, radio position finding systems generally fall into two classes, namely, continuous wave systems in which phase comparison of two or more space radiated waves is relied upon to produce the desired position information at a wave receiving point, and pulsed signal systems in which pulse transit time is the factor from which position information is derived.

In systems of the continuous wave type, the continuous waves radiated from a pair of spaced transmitters produce standing waves in space, the phase relationship of which changes as a function of changing position between the two transmitting points. More specifically, the standing waves produced by each pair of transmitting units of the system are characterized by isophase lines which are hyperbolic in contour about the transmitting points as foci. On a base line connecting the pair of transmitters, these isophase lines are spaced apart a distance equal to onehalf the mean wave length of the radiated waves and have diverging spacings at points on either side of this line. With this system arrangement, the position of a receiving point relative to a pair of hyperbolic isophase lines may be determined by measuring the phase relationship between continuous waves radiated from the pair of transmitters. Since the location of the receiving point along the zone separating the two isophase lines is not indicated by such a phase measurment, it becomes necessary to employ at least three spaced transmitters, different pairs of which function to provide a grid-like pattern of intersecting hyperbolic lines, in order to obtain absolute determination of the position of the receiving point. Systems of the character described are exceedingly accurate in so far as the the position indications produced at the 2 transmitters, or alternatively, so to arrange the system that phase shifts between the radiated waves are compensated during the phase comparing operation. Phase synchronization of the waves radiated from the plurality of transmitters presents an exceedingly diflicult problem which has been the subject of considerable development work. All solutions which have been found for this problem involve the use of relatively elaborate and somewhat delicate instrumentation not well adapted for the continuity of service required in position determining systems. To obviate this problem, systems of the continuous wave hyperbolic type have been proposed (see Honore Patent No. 2,148,267) in which the phase shift problem is obviated by heterodying the carrier waves of each pair of transmitters at a fixed link transmitting point, and modulating the difference frequency component of the heteroclyned waves as a reference signal upon the carrier output of the link transmitter for radiationto the receiving point, where the difference frequency component is detected and phase compared with a, difference frequency signal derived by directly heterodying the transmitted continuous waves at the receiving point. In this manner, phase shifts between the continuous waves radiated from the two transmitters are completely self-compensating so that the measured phase angle is truly representative of the location of the receiving point between a pair of equiphase lines. While the described arrangement for obviating the phase synchronization problem completely solves this'proble'm, it entails the use of two carrier channels for the link transmitters in addition to the three of four channels taken up by the three or four continuously survey transmitters, in order to make up a complete system. An improved arrangement for eliminating the link transmitterswithout eliminating the functions thereof is disclosed and claimed in the above referred to copending application. Another troublesome problem encountered in the operation of continuous wave system is that of eliminating ambiguity from the phase measurements which provide the desired position information. Thus while the two phase measurements identify the position of the receiving station relative to two intersecting pairs of hyperbolic isophase lines, they do not indicate which pairs of lines the indications are related to. This means that in operating the system, the geographic location of the receiving station must be known at the start of movement of this station relative to the transmitting stations, and

further that the lines must be counted as the receiving station is moved relative to the grid-like pattern of hyperbolic lines. It also means that a mobile craft entering the radiation pattern of the transmitters cannot utilize the radiated signals to determine its position without using auxiliary equipment to determine the approximate position of the craft relative to the position signal transmitters.

While pulsed signal radio position finding systoms of the type employing fixed position transmitting for radiating the pulsed position indicating signals, such, for example, as Loran, obviate the ambiguity problem inherent in phase comparison systems, they are generally much less accurate than phase comparison systems and hence are not well adapted for several types of survey work or navigation requiring highly accurate position data. Moveover, pulsed systems of the type referred to require synchronized pulse transmission from widely spaced pulse transmitters; a problem which is as 'diflicult to solve as that of phase synchronization in commercial types of phase comparison systems. In general, pulsed systems of the character described, like the phase comparison systems, are of the hyperbolic type in that lines representative of constant pulse transit time difference intervals are hyperbolic and have the transmitting points as foci. Both typm of hyperbolic systems require the use of specially prepared hyperbolic charts for the purpose of converting indications derived from the received position indicating signals into actual position data, making use of the constant velocity of propagation of radio waves.

It is an object of the present invention, therefore, to provide an improved radio position determining or ranging system which obviates substantially all of the problems outlined above.

It is another object of the invention to provide a combined pulse transit time and phase comparison system of position determination which is non-ambiguous, requires no synchronization whatever of the position indicating signals radiated by the transmitters, requires a minimum number of frequency channels and utilizes common transmitting and receiving equipment for the transmission and reception of the two types of position indicating signals, and in which the signals radiated by the transmitting equipment may be commonly received and utilized at any number of receiving stations.

It is a. further object of the invention to provide a combined pulse transit time and phase comparison position determining system which provides the accuracy of a phase comparison system and the non-ambiguity of a pulse system and requires only one coordinate chart for interpretation of the indications resulting from measurement of the phase relationship and pulse transit time difference intervals between a set of received signals.

In accordance with a more specific object of the invention facilities are provided in the system for establishing spacial coincidence between at least certain of the isophase lines and a corresponding portion of the constant pulse transit time difference interval lines which are eflective- 1y produced in space by the signals radiated from the transmitters of the system.

It is another and more general object of the ated by spaced transmitters of the system is not required.

It is still another object of the invention to provide improved and exceedingly simple receiving equipment for use in a combined pulse transit time and phase comparison position determining system of the character described.

It is a. still further object of the invention to provide an improved and exceedingly simple transmission system for use in a combined pulse transit time and phase comparison system of the character described.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the specification taken in connection with the accompanying drawings, in which:

Fig. 1 is a pictorial representation of a water covered area over which survey operations are to be performed, illustrating the positional arrangement of the transmitters embodied in the system and the grid-like system of isophase and constant pulse transit time difference interval lines effectively produced in space by the signals radiated by the transmitters;

Fig. 2 diagrammatically illustrates the component arrangement of the equipment provided at the transmitter units and one mobile receiving station or unit of the system shown in Fig. 1;

Fig. 3 is a time-signal pulse graph illustrated to facilitate explanation of the mode of operation of the system; and

Fig. 4-is an end perspective view of the electron beam tube provided at the illustrated receiving station to indicate pulse transit time difference intervals.

Referring now to the drawings and more particularly to Figs. 1 and 2 thereof, the present in vention is there illustrated in its embodiment in a combined pulse transit time and phase comparison system of position determination for providing position information aboard the boats of survey crews operating over a water covered area in part bounded by the illustrated shoreline segment 9. In brief, the system comprises three transmitting units III, II and I! which are spaced apart approximately equal distances along the shoreline 8 and are so positioned that the line 5b bisecting the base line connecting the units In and I I is angularly related to the line 6b bisecting the base line connecting the units II and I2. As described more fully below, the end transmitting units Ill and I! include transmitters for continuously radiating carrier wave signals of two different frequencies and the central transmitting unit ll comprises two transmitters which are controlled alternately to radiate periodic signal pulses of two still different frequencies, such that a system of standing waves or a standing signal pattern is effectively produced in space to blanket the area under survey. More specifically, the wave interference pattern produced by the signals radiated by the transmitter of the unit l0 and one of the transmitters of the unit I l during each interval when the latter transmitter is operating, 'is characterized by hyperbolic isophase lines 5 having the radiation points of the transmitting units Ill and II as tool. Similarly, the interference pattern produced in space by the signals radiated from the transmitter of the unit I 2 and the other transmitter of the central transmitting unit II during each period when the latter transmitter is operating, is characterized by hyperbolic isophase lines 6 having the radiation points of the transmitting units M and I2 as foci. Due to the angularv relationship between the base lines connecting the transmitting units |fi-i| and i|-| 2,

the two sets of hyperbolic isophase lines 5 and t intersect in the manner illustrated in Fig. 1 of the drawings to produce a grid-like pattern of intersecting hyperbolic lines. Superimposed upon this grid-like pattern of isophase lines is a second less thanhalf the-circumference of the ring. The

grid-like pattern of hyperbolic lines representatime through certain sections of the equipment provided at the two end transmitting ;units l and I2 is so controlled that the hyperbolic lines representative of predetermined constant pulse transit time difference intervals are spacially coincident with at least certain of the hyperbolic isophase lines 5 and B suchthat a single hyperbolic coordinate chart may be employed in converting phase comparison indications and pulse transit time difference intervals, as measured at any receiving station within the propagation range of the transmitting system, into position data.

As shown in Fig. 1 of the drawings, the system further comprises translating and receiving equipment generally designated as a mobile receiving station or unit l3 disposed'aboard each ec d boat 8 p rating in the .area under survey. In this connection, it may be pointed out that in certain types of survey work over water such, for example, as seismic survey operations, it is conventional practice to equip each survey crew with a recording boat on which all recording operations are performed. It may further be pointed out that any number of .mobile receiving stations or units |3 of the character shown in Fig. 2 of the drawings may utilize the signals originating at the transmitting'units II], II and |2 to obtain the desired positiondata.

Referring now more particularly to Fig. 2 of the drawings, the transmitter embodied in the unit I0 comprises a carrier Wave generator or oscillator I4 and a modulator and power amplifier unit I5. Similarly, the transmitter embodied in the transmitting unit [2 comprises a carrier wave oscillator or generator I! and a modulator and power amplifier unit l8. The transmitting unit comprises two transmitters 20 and 2| for respectively radiating pulsed position indicating carrier waves at two different carrier frequencies,

- lating segment 22a.-

remainder of the ring is comprised .ofan insuthe ring periphery. -Th'ese brushes are respectively connected to the positive bus conductors of the two transmitters 20 and 2|, such that anode current is alternately delivered to the electron discharge tubes of the two transmitters. Since the conductive segment 22b of the ring 22 represents slightly less than half the peripheral surface of the ring, it will be understood that a short off-signal period is provided between successive pulse periods during which the transmitters 20 and 2| are alternately operated, thus preventing simultaneous radiation of waves by both transmitters. The periodicity with which the two transmitters 20 and 2| are alternately operated is, of course, dependent upon the speed of rotation of the commutating ring 22. Preferably, this ring is driven at a speed of thirty revolutions per second such that the transmitters 23 and 2| are alternately rendered operative to generate pulsed signals at the rate of thirty pulses (of each signal) per second.

While thetransmitting unit H has been illustrated as comprising two transmitters 20 and 2|, it will be understood that if desired a single transmitter may be employed which is equipped with two carrier wave frequency determining elements, preferably crystals, having different resonant frequencies; In such case, the anodes of the tubes embodied in the transmitter may be continuously supplied with operating potentials in the usual manner, and the switching device comprising the commutating ring 22 may be employed alternately to'connect the two frequency determ ning elements into the transmitter circuit to control the output frequency of the transmitter.

.This arrangement has the advantage of minimizing duplication of equipment. It will also be understood that any desired switching arrangepose of rendering the transmitting unit alternately operative to transmit signal pulses of two difierentfrequencies.

the two transmitters 20 and 2| for alternate opquency spectrum by approximately kilocycles, the respective transmitters from the positive.ter-' minal of the anode current source, not shown,

eration is accomplished by alternately feeding anode current to the electron discharge tubes of gear train unit 23. More specifically, the positive terminal of the anode current source is con-- nected to the conductive segment 22b of the commutating ring 2, which segment spans slightly' As indicated above, the carrier frequencies at which the four transmitters of the three transmitting units I0, H and |2operate are all different. Specifically, the output frequency of the transmitter 20 and the output frequency of the transmitter in the unit ll), forming the first transmitter pair, may be 1700 and 17,40 kilocycles, respectively, such that the difference frequency therebetween is 40 kilocycles, while the output frequencies of the transmitter 2| and the transthus facilitating selective reception of these carrier pairs in the manner. more fully explained below. The power. of the four transmitters is such that the entire area in which position information may be desired aboard the vehicle or vessel carrying the receiving unit I3 is blanketed with waves radiated from each of the four transmitters and that these waves have a field strength atall points within this area sufiicient to permit At diametrically opposed points around the circumference of the'ring. .brushes 22c and 22d are provided which engage reliable reception without requiring undue sensitivity of the receiving equipment.

In order to obviate the above-mentioned difllculties attendant with phase synchronization of the position indication carrier waves and synchronization of the signal pulses radiated by the transmitters, while at the same time eliminating the necessity for utilizing additional frequency channels, means are provided in the transmitting units I and I2 for alternately modulating the waves radiated by the transmitters of theunits l0 and 12 with pulsed reference signals representative of the difference frequencies between the carrier wave pairs. These pulsed reference signals may be received at any receiving point such, for example, as at the mobile receiving unit l3, located within the radius of transmission of the four transmitters. The equipment for this purpose as provided at the transmitting unit l0 comprises a fixed tuned amplitude modulation receiver l6, center tuned to a frequency of 1930 kilocycles and having a response band broad enough to admit the 1900 and 1960 kilocycle signals respectively radiated by the transmitter 2| and the transmitter of the unit 12. The selectivity of this receiver is obviously such that the carrier waves radiated by the transmitter 20 and the transmitter of the unit III are rejected in the radio frequency sections thereof. The beat frequency of pulses of 60 kilocycles between the two carriers accepted by the radio frequency section of the receiver l6 are reproduced in the low frequency section of this receiver and delivered to the modulator for amplitude modulation upon the carrier output of the transmitter embodied in the unit I through a band pass filter 16a, which is center tuned to a frequency of 60 kilocycles, and pulse transit time delay means in the form of.- a pulse delay network lib. Similarly, the transmitting unit 12 is equipped with a fixed tuned amplitude modulation receiver is which is center tuned to a carrier frequency of 1720 kilocycles and has a, response band broad enough to accept the 1700 and 1740 kilocycle signals respectively radiated by the transmitter 20 and the transmitter of the unit 10. Here again, the selectivity of the receiver I9 is obviously such that the carrier waves radiated by the transmitter 2| and the transmitter of the unit I2 are rejected in the radio frequency sections of the receiver. The beat frequency pulses of kilocycles between the two carrier waves accepted by the receiver 19 are reproduced in the low frequency section thereof and modulated upon the carrier wave output of the transmitter embodied in the transmitting unit 12 through a band pass filter Isa which is center tuned to a frequency of 40 kilocycles and pulse transit time delay means in the form of a pulse delay network I9b.

Referring now more particularly to the equipment making up the receiving unit l3 at the mobile receiving station, it is pointed out that this equipment comprises a pair of fixed tuned amplitude modulation receivers 26 and 21 the output circuits of which are respectively connected through suitable amplifier and automatic gain or volume control stages 32 and 33 to a pair of phase angle meters 3t and 3| and a pair of narrow band pass filters 28 and 2!! center tuned respectively to frequencies of and 40 kilocycles. A time delay network 32a is interposed in the signal transmission path between the filter 28 and the phase meter 3|. Similarly, a time delay network 33a is included in the signal transmission path between the filter 23 and the phase meter 30. More specifically, the receiver 26 is fixed tuned to a carrier frequency of 1930 kilocycles and is designed to accept the pulsed signal radiated by the transmitter 2| and the carrier wave radiated by the transmitter of the unit l2 both when the latter is modulated and unmodulated. Similarly, the receiver 21 is fixed tuned to a carrier frequency of 1720 kilocycles and is designed to accept the pulsed signal radiated by the transmitter 20 and the carrier wave continuously radiated by the transmitter of the unit I0 both when the latter is modulated and unmodulated. The automatic gain control or AVC circuits associated with the amplifier stages 32 and 33 may be of any well known type capable of functioning without introducing amplitude distortion or variable phase shift in the reference signals and the heterodyne or difference frequency signals developed at the output terminals of the receivers 20 and 21. The time delay networks 32a and 33a are respectively provided in the receiving apparatus to compensate for the phase shift introduced into the beat frequency signal pulse translating channels of the transmitting units l0 and I2 by the pulse delay networks Nib and 1912. These delay networks are preferably of the adjustable delay type disclosed at pages 354 and 355 in "Radar Engineering by Fink, published by the McGraw-Hill Book Company in 1947. The filters 28 and 29, which may be of any standard commercial construction, perform the function of selecting the heterodyne or difference frequency signal pulses alternately developed at the output terminals of the receivers 26 and 21, respectively, and delivering these signals to the phase meters 3| and 30, respectively. These meters may be of the general character disclosed in Patent No. 1,762,725-Marrison, granted June 10, 1930, and are capable of measuring phase angles in excess of 360 electrical degrees between two impressed signal voltages. Each phase meter is equipped with a rotatable rotor carrying a pointer which indexes with a circular scale to indicate the phase relationship between the two impressed voltages. If desired, each meter may also be equipped with a revolution counter, gear driven from the rotor element of the meter to count the isophase lines traversed by the mobile receiving unit l3.

For the purpose of obtaining pulse transit time difference indications from the received signals in the manner more fully explained below, pulse transit time comparison means comprising an oscilloscope 35, a square wave oscillator 39, an electronic switching unit 36 and a pair of pulse shaping networks 31 and 38 are provided in the mobile receiving unit to respond to the pulsed signals originating at the transmitters of the units "I, II and I2. More specifically, the signal pulses developed at the output terminals of the receiver 26 are shaped to accentuate the pulse build-up of each pulse and sharpen the pulses in the pulse shaping network 31 and delivered to the terminals of the oscilloscope 35 through the electronic switching unit 36. Similarly, the signal pulses developed across the output terminals of the receiver 21 are shaped to accentuate the pulse build-up of each pulse and sharpen the pulses in the pulse shaping network 38 and delivered to the terminal of the oscilloscope through the electronic switching unit 36. Preferably, the pulse shaping networks 31 and 38 are of the character disclosed in Fig. 18.18a, page 501 in Radar System Engineering by Ridenour, published by the McGraw-Hill Book Company in 1947. The electronic switching unit 36 performs the function of alternately delivering signal pulse energy developed at the output terminals of the networks 31and 38 to the oscilloscope 35 and preferably is of the commercial type YE-9, manufactured by the General Electric Company of Schenectady, New York. The oscilloscope 35 is preferably of the commercial type 2'56-D, manufactured by Allen B. Dumont Laboratories, Inc. of Passaic, New Jersey. The square wave oscillator 39 is adjustable as to frequency by means comprising a frequency control element 39a and may be of any standard type. In cooperation with the horizontal magnetic defiection coils 35b and 350, which are externally located with respect to the tube 35a of the oscilloscope, this oscillator functions to confine the horizontal trace path of the cathode ray beam alternately to the zones A and B of the tube screen in the manner illustrated in Fig. 4 of the drawings.

In considering the operation of the above-described position determining system, it will be understood that when the motor and gear train unit 23 is operating to drive the commutating ring 22, anode current is alternately delivered to the electron discharge tubes of the transmitters 20 and 2|, such that these transmitters are alternately rendered operative to radiate carrier waves at frequencies of 1700 and 1900 kilocycles, respectively. The transmitters of the units l and i2, on the other hand, operate continuously. Accordingly, during each interval when the transmitter 20 is in operation, the carrier waves of 1700 and 1740 kilocycles respectively radiated by the transmitter 20 and the transmitter of the unit ID are picked up and heterodyned in the radio frequency sections of the receivers 19 and 21. In the receiver 19, the difference frequency signal pulse of 40 kilocycles is reproduced in the low frequency section of the receiver, passed by the filter l9a, delayed in time by the pulse delay network l9b and modulated upon the carrier wave output of the transmitter in the unit l2 for radiation as a reference signal pulse. If desired an amplifier and automatic gain control unit similar to the units 32 and 33 may be interposed in the output circuit of the receiver 19 in order to maintain constant modulation. The signal pulse modulated carrier wave radiated by the unit I2 is received by the receiver 25 of the mobile receiving unit l3 and the 40 kilocycle signal pulse is reproduced at the output terminals of this receiver. During the period indicated, the transmitter 2| is not in operation and hence no heterodyne or beat frequency signal pulse is developed by the receiver 26. The 40 kilocycle reference signal pulse as thus reproduced by the receiver 26 is amplified to the proper level in the amplifier and AVC stage 32 and applied to the right set of input terminals of the phase meter 33 and also to the input terminals of the 60 kilocycle band pass filter 28. This filter rejects the applied signal pulse and thus prevents the same from being applied to the right set of input term nals of the phase meter 3 I.

The 40 kilocycle beat frequency or heterodyne signal pulse resulting from heterodyning of the pulsed carrier radiated by the transmitter 20 with the continuous carrier radiated by the transmitter of the unit It] in the radio frequency section of the receiver 2! is reproduced across the output terminals of this receiver and after being amplified to the proper level in the amplifier and AVC stage 33 is applied to the left set ofterminals of the phase meter 3| and the input terminals of the 40 kilocycle band pass filter 29 in parallel. Since the filter 28 prevents a signal pulse from being applied to the right set of input terminals of the phase meter 3|, this phase meter does not respond to the signal voltage applied to its left set of input terminals by the receiver 21. The filter 29, however. passes the signal pulse developed across the output terminals of the receiver 21 and transmits the same through the delay network 33a to the left set of terminals of the phase meter '30. Thus two signal voltages of identical frequency and equal amplitude are applied to the two sets of input terminals of the phase meter 30, with the result that this phase meter functions accurately to measure the phase angle therebetween. This phase angle indication is accurately representative of the position of the receiving unit l3 between two isophase lines 5 of the standing wave pattern produced in space as a result of the carrier waves radiated by the transmitter 20 and the transmitter of the unit In.

To digress slightly at this point, it will be observed that during the above described operation, the 40 kilocycle reference signal pulse is applied to the right set of input terminals of the phase meter 30 directly from the amplifier and AVC stage 32, while the 40 kilocycle beat frequency signal applied to the left set of input terminals of the phase meter 30 from the amplifier and AVC stage 33 passes through the filter 29. It will also be observed that the reference signal pulse developed by the receiver l9, in traversing the modulation path of the transmitter in the unit 12, passes through the delay network l9b. No counterpart for the phase delay produced by the network [9b is included in the direct signal transit paths from the transmitter 20 and the transmitter of the unit In to the mobile receiving station l3. Thus, in the absence of the components I9a and 33a two non-matching and phase unbalancing networks 29 and l9b would be included in the respective signal input paths to opposite sides of the phase meter 30. As a consequence; minor changes in the signal frequency, say for example, from 40 kilocycles to 40.1 or 39.9 kilocycles, would result in non-compensating phase shifts in the two signal input paths of the phase meter circuit due to the phase shifting characteristics of the filter 29 and delay network [9b, thereby causing the phase meter 30 to give an erroneous indication. In the present improved system, however, such erroneous indications are prevented by providing means in the system for automatically compensating for undesirable phase shifts which could otherwise be produced in the filter 29 and the delay network l9a. This compensating means comprises the previously mentioned time delay network 33a, which is identical with the network |9b and incorporated in the left hand branch of the input circuit of the phase meter 39 between this meter and the filter 29, and the 40 kilocycle band pass filter 19a, identical with the filter 29 and included in the modulation path between the receiver I9 and the modulator and power amplifier unit l8. The filters I9a and 29 are adjusted to have identical phase shift characteristics and the same is true of the delay networks l9b and 33a.

As heretofore explained, the 40 kilocycle reference signal pulse applied to the right set of input terminals of the phase meter 30 is delivered to the modulator N3 of the unit l2 through the filter [911. Accordingly, any variation in the fre- 11 quency of this beat note signal pulse will cause a phase shift in the signal wave within the pulse identical to the phase shift produced in the filter 29. The reference signal pulse delivered to the modulator I8 also traverses the delay network ISb. However, any phase shift produced in the wave within the reference signal pulse in traversing this network is compensated by a corresponding phase shift in the signal pulse while traversing the delay network 88a. Thus, erroneous indications of the phase meter 80 are avoided.

At the end of the described transmitting interval, the commutating ring 22 functions to interrupt the circuit for delivering anode current to the tubes of the transmitter 20, with the result that carrier wave radiation from this transmitter is terminated. When radiation of this wave stops, the carrier heterodyning action of the two receivers l9 and 21 is likewise terminated to interrupt the reference signal pulse radiated by the transmitter of the unit l2 and to interrupt the heterodyne or difference frequency signal pulse being developed across the output terminals of the receiver 21. Thus the phase meter 80 is rendered ineffective further to change the setting of its indicating element.

A short time interval after operation of the transmitter 20 is stopped, the commutating ring 22 functions to deliver anode current to the tubes of the transmitter 2| and thus initiate operation of this transmitter. With the transmitter 2| in operation, a 1900 kilocycle position indicating signal pulse is radiated thereby which is accepted by the receivers l8 and 28. More specifically, the receiver l6 functions to heterodyne the pulsed carrier wave radiated by the transmitter 2| with the 1960 kilocycle carrier wave continuously radiated by the transmitter of the unit l2 and to reproduce the heterodyne or difference frequency signal of 60 kilocycles in the low frequency section thereof. This difference frequency or reference signal pulse is passed by the filter l6a, delayed in time by the network |8b, modulated upon the output carrier wave of the generator H in the modulator and power amplifier unit l5 and radiated as a modulation component upon the carrier wave transmitted by the transmitter of the unit In to the receiver 21. As previously mentioned in connection with the receiver |9 oi the unit |2, a suitable amplifier and automatic gain control stage may be interposed in the output circuit of the receiver It in order to maintain constant modulation. The receiver 21 accepts the signal pulse modulated carrier wave and reproduces the modulation component thereof in the usual manner. The reference signal pulse thus developed across the output terminals of the receiver 21 is amplified to the proper level in the amplifier and AVC stage 33 and applied across the-left set of input terminals of the phase meter 3| and the input terminals of the band pass filter 29 in parallel. This filter functions to reject the applied reference signal voltage and thus prevent the same from being impressed across the left set of input terminals of the phase meter 30. It will be understood that the receiver 21 is incapable of accepting the carrier waves radiated by the transmitter 2| and the transmitter of the unit |2. Hence this receiver is prevented from heterodyning the carrier waves radiated by either of these two transmitters with the carrier wave radiated by the transmitter of the unit Ill.

The 1900 and 1960 kilocycle waves respectively radiated by the transmitter 2| and the transmitter of the unit |2 are both accepted by the receiver 28 and heterodyned in the radio frequency section thereof to produce a 60 kilocycle heterodyne or difference frequency signal pulse which is reproduced across the output terminals of the receiver and, after amplification to the proper level in the amplifier and AVC stage 82, is applied to the right set of input terminals of the phase meter 88 and the input terminals of the filter 28 in parallel. Since no signal voltage is applied to the left set of terminals of the phase meter when the transmitter 2| is operating, this phase meter remains inactive. The reference signal pulse of 60 kilocycles. applied to the input terminals of the filter 28 is passed by this filter, delayed in time by the network 82a and applied to the right set of input terminals 7 of the phase meter 8|. Thus reference and heterodyne or difference frequency signal pulses of identical frequencies and equal amplitudes are respectively applied to the two sets of input terminals of the phase meter 8|. This phase meter functions to measure the phase relationship between the waves within the two applied signal pulses and thus provide an indication accurately representative of the position of the receiving unit I8 between two isophase lines 8 of the standing wave system effectively produced in space by the radiation of position indicating carrier waves from the transmitter 2| and the transmitter of the unit I2.

As previously described in connection with the circuits for the phase meter 38, but for the provision of the components lid and 82a, the input circuits to the phase meter 8| would be unbalanced in that the right hand branch would include the 60 kilocycle filter 28 and the left hand branch would effectively include the pulse delay network llib interposed in the modulation path between the receiver l8 and the modulator l5. Such unbalance would cause an undesirable phase shift in response to minor variations in the signal frequency for reasons explained above. The described unbalance is eliminated, however, by providing the filter l8a, identical with the 60 kilocycle filter 28, in the modulation path of the transmitter in the unit Ill, and by including the delay network 32a, identical with the delay network |6b in the modulation path of the transmitter in the unit l0, between the filter 28 and the right set of input terminals of the phase meter 3|. The two filters Mia and 28 are adjusted to have identical phase shift characteristics. Similarly, the delay networks lib and 32a are adjusted to have identical phase shift characteristics. Thus, erronous indications of the phase meter 3| due to changes in the frequency of the 60 kilocycle reference and heterodyne signal pulses are eliminated.

Another important reason for providing the filters lGa and l9a in the modulation paths of the transmitting units l0 and I2 is that of preventing interfering signals from being radiated by the transmitters of these two units. Thus with the transmitter 20 and the transmitter of the transmitting unit l8 operating, the output signal of the transmitting unit |2 consists of a 1960 kilocycle carrier wave modulated at 40 kilocycles. This signal is accepted by the receiver l5 and the 40 kilocycle modulation component is reproduced across the output terminals of the receiver. If the 60 kilocycle band pass filter |6a were not provided in the modulation path of the transmitting unit It, the described 40 kilocycle signal would be modulated upon the carrier radiated by the transmitting unit III and reproduced by the receiver 21 at the receivingstation I3 to interfere with the 40 kilocycle heterodyne signal being concurrently produced in the receiver 21 through direct heterodyning of the carrier waves received from the transmitter 20 and the transmitter of the transmitting unit l0. However, by-providing the filter l6a, the '40 kilocycle signal reproduced by the receiver I6 is blocked from the modulator l and hence is not radiated by the transmitter of the transmitting unit II). In a similar manner, the 40 kilocycle band pass filter |9a prevents spurious modulation of the carrier radiated by the transradiation of the 60 kilocycle reference signal pulse by the transmitter of the unit I0 and to terminate reproduction of the difference or heterodyne signal pulse at the output terminals of the receiver 26. Thus the application of signal voltages to the two sets of input terminals of the phase meter 3| is interrupted, with the result that no further change in the setting of the indicating element of this meter can be .produced. A short time interval after operation of the transmitter 2| is arrested, the commutating ring 22 functions to recomplete the circuit for delivering anode current to the tubes of the transmitter and thus reinitiate operation of this transmitter with the results described above.

From the foregoing explanation, it will be understood that the transmitters 20 and 2|, in their alternate operation to radiate pulsed carrier waves, cooperate with the receivers l9 and I6 of the transmitting units I2 and I0 alternately to render the transmitters of these latter units operative to radiate position indicating signal pulses and reference signal pulses. More in particular, the pulsed position indicating carrier waves alternately radiated by the transmitters 20 and 2| alternately cause the position indicating carrier waves respectively radiated by the transmitters of the units l2 and ID to be modulated with reference signal pulses during periods when these latter transmitters are respectively inactive as position indicating signal radiators. At the receiving station, the receivers 28 and 21 alternately detect and develop reference signal pulses and position indicating signal pulses which are amplified to equal amplitude levels in the stages 32 and 33 and supplied. to the phase meters and 3|.

In order to illustrate the action which occurs, arrow pointed solid lines have been shown in Fig.2 of the drawings to indicate the receiving points of signal acceptance and the sources of the accepted signals during each pulse period when the transmitter 20 is operating, arrow pointed dashed lines have been shown to illustrate the receiving points of signal acceptance and the sources of accepted signals during each pulse period when the transmitter 2| is operating, and arrow pointed dot-dash lines have been shown to illustrate signal pulse traversal of the signal translating channels of the units l0, l2 and I3. Further, certain of these lines have been labeled with the legends P1, P2, Pa and P4. to indicate the points of signal pulse acceptance in the receiving unit I3. The lines have also been suitably labeled with distinguishable pulse transit time designations for the purpose of more clearly describing the mode of operation of the pulse transit time comparison means provided in the mobile receiving unit or station I3. From a consideration of these lines and reflection upon the above explanation, it will be understood that the receivers 26 and 21 alternately function as reference signal pulse detecting receivers and as heterodyning receivers for developing the ,required heterodyne or difference frequency signal pulses. Specifically, the receiver 26 functions as a heterodyne receiver in respect to the position indicating carrier waves radiated by the transmitter 2| and the transmitter of the unit I2, and functions as a reference signal pulse reproducing receiver in receiving the reference signal pulse modulated carrier radiated by the transmitter of the unit |2. The receiver 21, on the other hand, functions as a heterodyne receiver in respect to the position indicating carrier waves radiated by the transmitter 20 and the transmitter of the unit l0 and as a reference signal pulse detecting receiver in receiving the reference signal pulse modulated carrier wave radiated by the transmitter of the unit If].

As will also be evident from the above explanation, the phase meter 30 functions to produce a phase angle indication which is representative of the position of the receiving unit l3 between two isophase lines 5 of the standing waves produced in space as a result of carrier wave radiation by the transmitter 20 and the transmitter of the unit l0. With the described arrangement, wherein carrier wave frequencies of 1700 and 1740 kilocycles are employed, the wavelength spacing between the isophase lines along the base line connecting the units In and H is determined by the mean frequency of 1720 kilocycles between the two radiated carrier waves. At this particular mean frequency, isophase lines 5 representative of the same phase relationship between the standing waves produced by the transmitter 20 and the transmitter of the unit Ill along the base line joining the units I0 and H are spaced apart a distance of about 286 feet. Hence the indication provided by the phase meter 3|] identifies the position of the receiving unit I3 within a zone not less than 286 feet in width, i. e., a zone having a minimum width equal to one half the wavelength of a wave having a frequency equal to the mean frequency of the position indicating carrier waves radiated by thetransmitter 20 and the transmitter of the unit I0.

As previously indicated, the indication pro vided by the phase meter 30, standing alone, is ambiguous for the reason that this indication does not identify the point of location of the receiving unit I3 along the zone separating the two adjacent isophase lines 5 of the standing waves produced in space by the transmitter 20 and the transmitter of the unit l0. Identification of this point is obtained through the response of the receiving unit to the position indicating signal pulses radiated by the transmitter 2| and the transmitter of the unit |2. Thus, the phase meter 3| provides an indication of the position of the receiving station, namely the unit l3, between two isophase lines 6 of the standing waves effectively produced in space by the radiation of position indicating carrier waves from the transmitter 2| and the transmitter of the unit l2. Here again, the wavelength spacing of the isophase lines 6 along the base line connecting the two units II and I2 is determined by the mean frequency of 1930 kilocycles between the frequencies of the waves radiated by the transmitter 2I and the transmitter of the unit I2. At this particular mean frequency, isophase lines representative of the same phase relationship between the standing waves produced by the two identified transmitters have a minimum spacing of approximately 255 feet, such that the indication provided by the meter 3| identifies the position of the receiving unit I3 within a zone having a minimum width of 255 feet. The two indications thus provided by the phase meters 30 and 3I may readily be converted to position data by consulting a hyberbolic chart showing the hyperbolic isophase lines 5 and 6 in their geographic relationship to the known radiation points of the transmitting units I0, II and I2.

As previously indicated herein, although the position indications provided by the two phase meters identify the position of the receiving unit I3 relative to the isophase lines 5 and 6 with extreme accuracy, they are ambiguous in the sense that they do not identify the particular lanes between these lines in which the signals are collected at the receiving unit I3. Hence, unless the starting point of the unit I3 is known and the lanes are counted as the station is moved about within the area of signal radiation from the three transmitting units III, II and I2, the indications provided by the two phase meters cannot be interpreted to identify the position of the receiving unit I3. I

In accordance with the present invention, the ambiguity of the indications provided by the phase meters 30 and 3I is resolved by utilizing the pulse transit time comparison means comprising the oscilloscope 35, the square wave oscillator 39, the switchingunit 36 and the two pulse shaping networks 31 and 38 to measure the time differences between the sigal pulses developed across the output terminals of the two receivers 26 and 21. In this regard it will be recalled that the transmitters in the units I0 and I2 are in continuous operation and alternately serve as heterodyning signal sources for the pulsed signals originating at the transmitting unit. Thus the signal pulses all originate at a common point, namely the radiation point of the transmitting unit I I. Each pulse is transmitted to the receivingunit I3 over two diil'erent routes. Thus each signal pulse radiated by the transmitter 20 is directly transmitted to the receiver 21 and is in transit between the transmitter 20 and the receiver 21 a variable time interval Ta determined solely by the distance =between the radiation point of the transmitting unit I I and the signal collecting point 01' the receiving unit I3. These pulses are identified as the pulses P1 and each thereof traverses the signal translating channel through the components 21, 38, 36 and 35 in the time interval Tz. Each pulse radiated by the transmitter 20 is also transmitted to the receiver I9 in a pulse transit interval Tb, traverses the receiver translating channel and the modulation path of the transmitting unit I2- in the transit interval TX is transmitted to the receiver 26 of the receiving unit I3 in the transit interval To and traverses the signal translating path through the components 26, 31, 36 and 35 in the time interval Ty. The pulses traversing this path are identified as the pulses P2. Prefeerably the components 26, 21, 35, 36, 31 and 38 are 16 so designed that the pulse transit intervals Ty and T; are equal. Each of the intervals T, and T. is constant. The pulse transit interval Tb is constant and is determined by the length 01 the base line connecting the transmitting units II and I2. For any given adjustment of the delay network I9b, the pulse transit interval T; is also TD=Tb+Tx+Tc+TyTa-Tz However,

Tb+ Tx+ Ty- Tz=K=a constant time interval (2) Therefore, TD=K+ Tc-T. (3)

It can easily be shown that Equation 3 above is the equation of a hyperbola. Hence it will be understood that the locus of all points representative of a given constant pulse transit time difference interval is a hyperbola having the radiation points of the transmitter 20 and the transmitter of the unit I2 as fool, and that spaced apart hyperbolic lines all having the radiation points of these transmitters as tool are representative of different constant pulse transit time difference intervals.

In a similar manner, each signal pulse radiated by the transmitter H is directly transmitted to the receiver 26 and is in transit between the transmitter 2I and the receiver 26 a variable time interval Tn determined solely by the distance between the radiation point of the transmitting unit I I and thesignal collecting point oi the receiving unit I3. These pulses are identified as the pulses P3 and each traverses the signal translation channel through the components 26, 31, 36 and 35 in the time interval Ty. Each pulse radiated by the transmitter 2I is also transmitted to the receiver I6 in a pulse transit interval Tm, traverses the receiver translating channel and the modulation path of the transmitting unit I6 in the transit interval Tn is transmitted to the receiver 21 of the receiving unit I3 in the transit interval T01 and traverses the signal translating path through the components 21, 33,- and 35 in the time interval Ts. The pulses traversing this path are identified as the pulses P4. The pulse transit interval Tm is constant and is determined by the lengthoi' the base line connecting the transmitting units I0 and II. For any given adjustment of the pulse delay network IN), the pulse transit interval Txl is also a constant. The pulse transit interval T61 is a variable determined by the distance between the signal radiation point of the transmitting unit III and the signal collection point of the receivingunit I3. Thus in considering any given signal pulse radiated by the transmitter 2|, the pulse transit diil'erence time TD1, as measured by the oscilloscope 35, between the pulse as reproduced by the receiver 26 and later by the receiver 21 may be represented by the equation:

TD1= Tbl Tzl+ Tcl+ Tr- Tal- Ty However,

Tz 1+T=1+T=Ti/=K1=a constant time interval 17 Therefore, TD1=K1+Tc1-Tai (6) It can easily be shown that Equation 6 above is the equation of a hyperbola. It will .be understood, therefore, that the locus of all points representative of a given constant pulse transit time difference interval, as between the transit times required for the pulse originating at the transmitter 2| to reach the receiving unit I3 over the two paths, is a hyperbola having the radiation points of the transmitter 2| and the transmitter of the unit it as tool, and further that spaced apart hyperbolic lines all having the radiation points of these two transmitters as foci are representative of different constant pulse transit time difference intervals. Referring now more particularly to the manner in which the electronic switching unit 36 and the square wave oscillator 39 control visual reproduction of the signal pulses by the cathode ray tube 35a of the oscilloscope 35, it is pointed out above that the switching unit 38 alternately derives signal pulse energy from the two pulse shaping networks 38 and 31 and delivers this energy to the vertical deflection electrodes of the tube 35a through the signal channel of the oscilloscope. Further, by suitable adjustment of the balance control means provided in the switching unit 35, vertical separation of the visually reproduced signal pulses is eifected in the manner illustrated in Fig. 4 of the drawings. Hence when two signal pulses are received from the two pulse shaping networks 38 and 31 during a horizontal trace .period of the oscilloscope, they are reproduced one above the other on the screen of the cathode ray tube 35a. The frequency ofswitching of the electronic switching unit 36 is extremely high in comparison with the sweep repetition rate of the oscilloscope 35, being preferably of the order of Ill switching cycles per second. The sweep repetition rate of the oscilloscope 35 is adjusted to a value exactly twice the rate of switching of the transmitters 20 and 2|, 1. e., 60 sweep cycles per second.

During operation of the equipment, the square wave oscillator 39 and the horizontal amplifier in the oscilloscope 35 cooperate to restrict the length of the beam trace paths horizontally of the cathode ray screen alternately to the zones A and B as shown in Fig. 4 of the drawings, such that the'pulses P1 and P2 received at the receiving unit l3 over the two different paths from the transmitting unit II when the transmitter 20 is operating are reproduced in the beam trace zone A to the left of the cathode ray tube screen, whereas the pulses Pa and P4 received at the receiving unit 13 over the two different paths from the transmitting unit I I when the transmitter 2| is operating are reproduced in the beam trace zone B. More specifically, and as indicated in Fig. 2 of the drawings, during each alternate half cycle a. of the signal voltage impressed upon the deflecting coils 35b and 35c by the square wave oscillator 39, the beam trace path of the tube 35a horizontally oflthe cathode ray tube screen is confined to the zone A. During the intervening half cycles 1) of the signal voltage impressed upon the deflecting coils 35b and 350 by the oscillator 39, horizontal deflection of the cathode ray relative to the screen of the tube is confined to the beam trace zone B. By suitable adjustment of the frequency adjusting element 33aof the oscillator 39, the output frequency of this oscillator is adjusted precisely to equal the frequency at which the transmitond, it will be understood that the initial portion ters 20 and 2! are switched at the transmitting unit l I, i. e., to a value of 30 cycles per second.

From the above explanation and reference to Fig. 4 of the drawings, it will be understood that during each period when the transmitter 20 is operating to cause development of the pulses P1 and P2 across the output terminals of the pulse shaping networks 38 and 31, respectively, horizontal deflection of the cathode ray beam in the tube 35a is confined to the zone A. As the two pulses Pi and P2 are developed at the output sides of the networks 38 and 31, the electronic switching unit, which is operating at an extremely high switching frequency, causes successive small increments of each pulse to be reproduced visually on the screen of the tube 35a within the beam trace zone A. Moreover, due to the unbalanced setting of the balance control means embodied in the switching unit 36, the reproduced increments of the signal pulses are displaced vertically on the screen. Thus, during each horizontal sweep of the cathode ray beam, at least the initial .portions of the two pulses P1 and P2 are reproduced on the screen within the zone A thereof. After the time of one-half cycle of the square wave oscillator 39 has elapsed, this oscillator operating in conjunction with the deflection coil 35b and 350 deflects the beam of the tube 35a to confine horizontal deflection thereof to the zone B. During the interval when the cathode ray beam is confined to the zone B, the transmitter 2| operates in the manner explained above to cause development of the pulses P3 and P4 across the output terminals of the pulse shaping networks 31 and 38, respectively. Here again, the rapid switching of the oscilloscope input terminals between the output sides of the two networks 31 and 38 causes reproduction of the pulses Pa and P4 in small increments. However, ever the elapsed time of the horizontal beam sweep in progress, at least the initial portions of both pulses are reproduced on the screen within the zone B thereof. Since each of the pulses Pl, P2, P3 and P4 is developed at the transmitting unit ll at the rate of 30 pulses per secof each pulse is reproduced on the screen of the cathode ray tube 35a at the same rate. Due to the persistence of vision of the human eye, and the image persistence of the fluorescent screen of the tube 35a, the initial portions of the four signal pulses continuously persist on the screen in the four different positions described.

From an examination of Fig. 4 of the drawings,

it will be seen that the time delay TD between the initial portions of the pulses P1 transmitted directly from the transmitter 20 of the transmitting unit H to the receiving unit [3 over the path Ta and the initial portions of the pulses P: transmitted from the transmitter 20 to the receiving unit [3 by way of the transmitting unit I2 is accurately indicated by the horizontal displacement D between the starting points of the pulses'Pr and P2. Similarly, the time delay 'I'D1 between the initial portions of the pulses Pa transmitted directly to the receiving unit I3 from the transmitter 2| over the path Ta]. and the initial portions of the pulses P4 transmitted to the receiver unit l3 from the transmitter 2| by way of the transmitting unit In is accurately indicated by the horizontal displacement Dr between the starting points of the pulses P3 and P4. At this point it is noted that since the pulses P3 are received directly at the receiver 26 of the receiving unit l3 from the transmitter 2! of the transmitting 19 unit ll, they are reproduced beneath the pulses P4 which are received at the receiving unit I! indirectly from the transmitter 2| by way of the transmitting unit l0. By proper interpretation of the measured delay intervals TD and TDl,

through the use of hyperbolic coordinate charts having intersectin hyperbolic lines representative of constant pulse transit time diiference intervals and having the known radiation points of the transmitting units III, II and I! as fool, the exact geographic location of the receiving unit l3 may easily be determined.

Referring again to the pulses produced by the transmitter 20, it will be understood that reception and reproduction of each pulse P1 by the receiver 21 and pulse shaping network 38 is started before reception and reproduction of the corresponding pulse P: by the receiver 26 and pulse shaping network 31 so long as the pulse transit interval T. does not exceed the total time represented by the pulse transit time intervals Tb, Tx and Te. However, in certain locations of the receiving unit l3 relative to the radiation points of the transmitting units It, H and ii, the pulse transit interval T. may be greater than the total time interval represented by the pulse transit intervals '11,, TX and Tc. In such case, the initial portions of the pulses P: are reproduced to the left of the initial portions of the pulses P1 within the zone A of the cathode ray tube screen. However, the relative vertical positions of the reproduced pulses P1 and P: remain the same. Obviously, if the pulses originating at the transmitter 20 require exactly the same amount of time to reach the receiving unit l3 over the two different paths, the pulses P1 and P2 are reproduced one above the other in exact vertical alignment. The same is true of the relative horizontal positions of the reproduced pulses Pa and P4. Thus the system arrangement is such that positive identification of the paths over which the pulses are transmitted to the receiving unit I3 is assured.

Referring again to Equations 2 and 4 above, it can be shown that the disposition of any particular hyperbolic line representative of a predetermined constant pulse transit time difl'erence interval relative to the radiation points of the two spaced transmitters is determined by the constant K as regards Equation 2 and the constant K1, as regards Equation 4. Considering Equation 2 by way of example, the constant K is partially determined by the transit time Tb which in turn depends upon the distance between the transmitting units I i and I2 and hence cannot conveniently be varied. However, this constant is also determined by the transit time Tx, which may be varied as desired by suitable adjustment of the pulse delay network 19b. Preferably, this factor T! is so adjusted that the constant pulse transit time difference interval line bisecting the base line between the radiation points of the transmitting units I I and I2 is a straight line spacially coincident with the isophase line 6b. Similarly, the pulse delay network 16b is preferably so adjusted that the transit interval Tn produces a constant pulse transit time diil'erence interval line in space which bisects the base line between the radiation points of the transmitting units II and II and is spacially coincident with the isophase line 5b. When the straight pulse transit time difference interval lines are thus brought into spacial coincidence with the straight isophase lines 5b and 6b, the families of phase and pulse transit time difference interval hyperbolas are properly orientated with respect to each other. Hence each isophase line 5 is also representative of the locus of all points of a constant pulse transit difference interval and the same is true of each isophase line 6. Accordingly, each of the illustrated hyperbolic lines 5 and 6 may be used for the dual purpose of interpreting phase and pulse transit time indications. Thus, a single coordinate chart may be used at the receiving unit lit to interpret the indications provided by the phase meters and 3| and also by the oscilloscope 35.

From the foregoing explantion, it will be understood that in the present improved system, the problem of synchronizing pulses developed at two or more widely separated transmitting points is completely obviated. The system has the further advantage that harmonic relationships between the signals developed at two or more transmitting points of the system are not required. Also, the

system arrangement is-such that standard com- I more important is the fact that while the system least one of said signals, and pulse transit timeis characterized by the precision accuracy inherent in phase comparison systems of position determination, it also embodies the highly desirable feature of non-ambiguity inherent in pulsed systems of position determination. The system is further characterized by the described novel arrangement whereby a single coordinate chart may be employed in converting the phase and pulse transit time indications into position data. Moreover, the arrangement of the system is such that the three transmitting units thereof may be left completely unattended. Further, the signals radiated by these transmitting units may be received and translated at any number of receiving units l3 operating within the area of transmission of the three transmitting units. Thus the system is essentially a multi-user system.

While one embodiment of the invention has been described, it will be understood that various modifications may be made therein which are within the true spirit and scope of the invention as defined in the appended claims.

What is desired to be secured by United States Letters Patent is: v

1. A combined pulse transit time and phase comparison system of position determination, comprising transmitting apparatus for concurrently producing pulsed signals for phase and pulse transit time comparison, and receiving apparatus remote from at least a portion of said transmitting apparatus and including phase measuring means and pulse transit time comparison means both responsive to said signals for producing separate indications representative of the position of said receiving apparatus relative to at least one of the sources of said signals.

2. A combined pulse transit time and phase comparison system of position determination, comprising a receiving station, transmitting apparatus for concurrently producing pulsed comparison means at said receiving station responsive to the transmission of said pulsed signals to said receiving station over said two different paths for producing a second indication representative of the position of said receiving station relative to the source of at least one of said signals.

3. A combined pulse transit time and phase comparison system of position determination, comprising transmitting apparatus for radiating a plurality of signals and including means for pulsing at least one of said signals, said signals efiectively producing standing waves in space characterized by space isophase lines and also by spaced lines representative of different constant pulse transit diiference intervals, and a receiving station including means excited by said signals and separately controlled in accordance with the phase relationship between said waves and the pulse transit difference intervals for producing a plurality of separate indications representative of the position of said receiving station relative to certain of said lines.

4. A combined pulse transit time and phase comparison system of position determination, comprising transmitting apparatus for radiating a plurality of signals and including means for pulsing at least one of said signals, said signals effectively producing standing waves in space characterized by spaced isophase lines and also by spaced lines representative of different constant pulse transit difference intervals, a receiving station including means excited by said signals and separately controlled in accordance with the phase relationship between said waves and the pulse transit difierence intervals for producing a plurality of separate indications representative of the position of said receiving station relative to certain of said lines, and means included in said system for establishing spacial coincidence between at least a portion of said spaced isophase lines and a corresponding portion of the lines representative of different con stant pulsertransit difference intervals.

5. A combined pulse transit time and phase comparison system of position determination, comprising transmitting apparatus for radiating a plurality of signals and including means for pulsing at least one of said signals, said signals eilectively producing standing waves in space characterized by spaced isophase lines and also by spaced lines representative of difierent constant pulse transit difference intervals, means included in said transmitting apparatus for establishing spacial coincidence between at least a portion of said spaced isophase lines and a corresponding portion of the lines representative of difierent constant pulse transit difference intervals, and a receiving station including means excited by said signals and separately controlled in accordance with the phase relationship between said waves and the pulse transit difference intervals for producing a plurality of separate indications representative of the position of said receiving station relative to certain of said lines.

6. A combined pulse transit time and phase comparison system of position determination, comprising transmitting apparatus for radiating a plurality of signals from at least three spaced transmitting points and including means for pulsing at least one of said signals, said signals effectively producing standing waves in space characterized by two intersecting sets of spaced hyperbolic isophase lines having different pairs of said transmitting points as fool and also by two intersecting sets of spaced hyperbolic lines representative of different constant pulse transit difierence intervals which also v have said different pairs of transmitting points as foci, and a receiving station including means excited by said waves and' separately controlled in accordance with the phase relationship between said waves and the pulse transit difierence intervals for producing a plurality of separate indications representative of the position of said receiving station relative to certain of said hyperbolic lines.

7. A combined pulse transit time and phase comparison system of position determination, comprising transmitting apparatus for radiating a plurality of signals from at least three spaced transmitting points and including means for pulsing at least one of said signals, said signals efiectively producing standing waves in space characterized by two intersecting sets of spaced hyperbolic isophase lines having different pairs of said transmitting points as foci and also by two intersecting sets of said spaced hyperbolic lines representative of different constant pulse transit difference intervals which also have said different pairs of transmitting points as foci, 'a receiving station including means excited by said waves and separately controlled in accordance with the phase relationship between said waves and the pulse transit diflerence intervals for producing a plurality of separate indications representative of the position of said receiving station relative to certain of said hyperbolic lines, and means included in said system for establishing spacial coincidence between at least a portion of said hyperbolic isophase lines and a corresponding portion of the hyperbolic lines representative of different constant pulse transit difierence intervals.

8. A combined pulse transit time and phase comparison system of position determination, comprising transmitting apparatus for radiating a plurality of signals from at least three spaced transmitting points and including means for pulsing at least one of said signals, said signals efi'ectively producing standing waves in space characterizedby two intersecting sets of spaced hyperbolic isophase lines having different pairs of said transmitting points as foci and also by two intersecting sets of spaced hyper-bolic lines representative of different constant pulse transit difference intervals which also have said difierent pairs of transmitting points as tool means included in said transmitting apparatus for establishing spacial coincidence between at least a portion of said hyperbolic isophase lines and a corresponding portion of the hyperbolic lines representative of difierent constant pulse transit difference intervals and a receiving station including means excited by said signals and separately controlled in accordance with the phase relationship between said waves and the pulse transit difference intervals for producing a plurality of separate indications representative of the position of said receiving station relative to certain of said lines. Y

9. A combined pulse transit time and phase comparison system of position determination, comprising a receiving station, transmitting apparatus including transmitters for concurrently radiating signals of different frequencies and means for pulsing one of said signals, a reference signal repeating station remote from said receiving station, means at each of said stations for heterodyning said signals to produce signal pulses having a frequency related to the beat frequency between the heterodyned signals, means for transmitting the signal pulses produced at said repeating station to said receiving station, phase measuring means at said receiving station excited by said signal pulses for producing one indication representative of the position of said receiving station relative to said repeating station, and pulse transit time comparison means at said receiving station excited by said signal pulses for producing a second indication representative of the position of said receiving station relative to said repeating station.

10. A combined pulse transit time and phase comparison system of position determination, comprising a receiving station, transmitting apparatus including transmitters for concurrently radiating signals of different frequencies and means for pulsing one of said signals, a reference signal repeating station remote from said receiving station, means at each of said stations for heterodyning said signals to produce signal pulses having a frequency related to the beat frequency between the heterodyned signals, means 'for transmitting the signal pulses produced at said repeating station to said receiving station, pulse transit time comparison means at said receiving station responsive to the time difference between the signal pulses developed locally at said receiving station and the signal pulses transmitted to said receiving station from said repeating station for producing one indication representative of the position of said receiving station relative to said repeating station, and phase measuring means at said receiving station responsive to the phase relationship between the waves within the signal pulses developed locally at said receiving station and the waves within the signal pulses transmitted to said receiving station from said repeating station for producing a second indication represenative of the position of said receiving station relative to said repeating station.

11. A combined pulse transit time and phase comparison system of position determination, comprising a receiving station, transmitting apparatus including transmitters for concurrently radiating signals of different frequencies and means for pulsing one of said signals, a reference signal repeating station remote from said receiving station, means at each of said stations for heterodyning said signals to produce signal pulses having a frequency related to the beat frequency between the heterodyned signals, means for transmitting the signal pulses produced at said repeating station to said receiving station, phase measuring means at said receiving station responsive to the phase relationship between the waves within the signal pulses developed locally at said receiving station and the waves within the signal pulses transmitted to said receiving station from said repeating station for producing a highly accurate but ambiguous indication representative of the position of said receiving station relative to said repeating station, and pulse transit time comparison means at said receiving station responsive to the time diflerence between the signal pulses developed locally at said receiving station and the signal pulses transmitted to said receiving station from said repeating station for producing a non-ambiguous but less accurate indication representative of the pos tion 12. A combined pulse transit time and phase comparison system of position determination,

comprising two transmitters for radiating signals at different frequencies and at spaced radiation points, transmitting means for radiating pulsed signals alternately at two still different frequencies from at least one additional radiation point, means responsive to said pulsed signals for alternately modulating the signals radiated by said two transmitters with reference signal pulses, said radiated signals eflectively producing standing waves in space characterized by two intersecting sets of spaced hyperbolic isophase lines having dlii'erent pairs of said transmitting points as foci and also by two intersecting sets of spaced hyperbolic lines representative of difierent constant pulse transit difference intervals which also have said different pairs of transmitting points as foci, and a receiving station including means responsive to said signals and separately controlled in accordance with the phase relationship between said waves and the pulse transit difference intervals for producing a plurality of separate indications representative of the position of said receiving station relative to certain of said lines.

13. A combined pulse transit time and phase comparison system of position determination, comprising two transmitters for radiating signals at different frequencies and at spaced radiation points, transmitting means for radiating pulsed signals alternately at two still difierent frequencies from at least one additional radiation point, means responsive to said pulsed signals for alternately modulating the signals radiated by said two transmitters with reference signal pulses, said radiated signals effectively producing standing waves in space characterized by two intersecting sets of spaced hyperbolic isophase lines having diiferent pairs of said transmitting points as foci and also by two intersecting sets of spaced hyperbolic lines representative of different constant pulse transit difference intervals which also have said different pairs of-transmitting points as foci, means included in said system for establishing spacial coincidence between at least a portion of said hyperbolic isophase lines and a corresponding portion of the hyperbolic lines representative of different constant pulse transit difference intervals, and a receiving station including means responsive to said signals and separately controlled in accordance with the'phase relationship between said waves and the pulse transit diflerence intervals for producing a plurality of separate indications representative of the position of said receiving station relative to certain of said lines. Y

14. A combined pulse transit time and phase comparison system of position determination, comprising two transmitters for radiating signals at different frequencies and at spaced radiation points, transmitting means for radiating pulsed signals alternately at two still different frequencies from at least one additional radiation point, means responsive to said pulsed signals for alternately modulating the signals radiated by said two transmitters with reference signal pulses, said radiated signals efiectively producing standing waves in space characterized by two intersecting sets of spaced hyperbolic isophase lines having different pairs of said transmitting points as foci and also by two intersecting sets of spaced hyperbolic lines representative of different constaat Pu s transit diilerence interva s which al o have said diflerent pairs of transmitting points as foci, reference pulse transit time control means interposed in the paths of modulation of said two transmitters for establishing spacial coincidence between at least a portion of said hyperbolic isophase lines and a corresponding portion of the hyperbolic lines representative of different constant pulse transit difierence intervals, and a receiving station including means responsive to said signals and separately controlled in accordance with the phase relationship between said waves and the pulse transit diflerence intervals for producing a plurality of separate indications representative of the position of said receiving station relative to certain of said lines.

15. A position determining system, comprising a receiving station, transmitting means for transmitting pulsed wave trains to said receiving station over two difierent paths, and receiving and translating apparatus at said receiving station including phase measuring means responsive to said waves for producing one indication representative of the position of said receiving station relative to said transmitting means, and pulse excited means responsive to the pulsing of said wave trains for producing a second indication repre-,

sentative of the position of said receiving station relative to said transmitting means.

16. A position determining system, comprising a receiving station, transmitting means for transmitting wave trains to said receiving station over two different paths, means common to said paths for pulsing said wave trains in unison, and receiving and translating apparatus at said receiving station including means responsive to the time displacement between corresponding pulses of said wave trains for producing one indication representative of the position of said receiving station relative to said transmitting means, and phase measuring means responsive to the waves within the pulses for producing a second indication of the position of said receiving station relative to said transmitting means.

17. A combined pulse transit timeand phase comparison system of position signal transmission, comprising transmitting apparatus for radiating a plurality of signals and including means for pulsing at least one of said signals, said signals efiectively producing standing waves in space characterized by spaced isophase lines and also by spaced lines representative of diiferent constant pulse transit difierence intervals, and means included in said system for establishing spacial coincidence between at least a portion of said spaced isophase lines and a corresponding portion of the lines representative of difierent constant pulse transit difl'erence intervals.

18. A combined pulse transit time and phase comparison system of position signal transmission, comprising transmitting apparatus for radiating a. plurality of signals from at least three spaced transmitting points and including means for pulsing at least one of said signals, said signals effectively producing standing waves in space characterized by two intersecting sets of spaced hyperbo'ic lines having difierent pairs of said transmitting points as foci and also by two intersecting sets of spaced hyperbolic lines representative of difi'erent constant pulse transit difierence intervals which also have said difierent pairs of said transmitting points as foci, and means included in said system for establishing spacial coincidence between at least a'portion of said hyperbolic isophase lines and a corresponding portion of the hyperbolic lines representative of 26 different constant pulse transit difierence intervals.

19. A transmission system for a combined pulse transit time and phase comparison system of position determination, comprising a first transmitter for continuously radiating a first signal of one frequency, a second transmitter for radiating a pulsed signal of different frequency, a third transmitter for radiating a carrier signal at a third frequency, heterodyning means for heterodyning said first and pulsed signals to produce a pulsed reference signal having a frequency related to the beat frequency between said first and pulsed signals, and modulating means for modulating said pulsed reference signal upon the carrier signal radiated by said third transmitter, said signals effectively producing standing waves in space characterized by spaced hyperbolic isophase lines having the radiation points of said first andsecond transmitters as fuel and also by spaced hyperbolic lines representative of difierent constant pulse transit difference intervals which have the radiation points of said second and third transmitters as tool.

20. A transmission system for a combined pulse transit time and phase comparison system of position determination, comprising a first transmitter for continuously radiating a first signal of one frequency, a secondtransmitter for radiating a pulsed signal of diflerent frequency, a third transmitter for radiating a carrier signal at a third frequency, heterodyning means for heterodyning said first and pulsed signals to produce a pulsed reference signal having a frequency related to the beat frequency between said first and pulsed signals, modulating means for modulating said pulsed reference signal upon the carrier signal radiated by said third transmitter, said signals efiectively producing standing waves in space characterized by spaced hyperbolic isophase lines having the radiation points of said first and second transmitters as tool and also by spaced hyperbolic lines representative of difierent constant pulse transit difference intervals which have the radiation points of said second and third transmitters as foci, and means included in said system for determining the spacial disposition of at least certain of said hyperbolic lines.

21. A transmission system for a combined pulse transit time and phase comparison system of position determination, comprising a first transmitter for continuously radiating a first signal of one frequency, a second transmitter for radiating a pulsed signal of difierent frequency, a third transmitter for radiating a carrier signal at a third frequency, heterodyning means for heterodyning said first and pulsed signals to produce a pulsed reference signal having a frequency related to the beat frequency between said first and pulsed signals, modulating means for modulating said pulsed reference signal upon the carrier signal radiated by said third transmitter, said signals eii'ectively producing standing waves in space characterized by spaced hyperbolic isophase lines having the radiation points of said first and second transmitters as tool and also by spaced hyperbolic lines representative of different constant pulse transit difference intervals which have the radiation points of said second and third transmitters as foci, and reference pulse transit time control means interposed between said heterodyning means and said modulating means to determine the spacial disleast one additional radiation point, and means responsive to said pulsed signals for alternately modulating the signals radiated by said two transmitters with reference signal pulses, said radiated signals effectively producing standing waves in space characterized by two intersecting sets of spaced hyperbolic isophase lines having different pairs of said transmitting points as foci and also by two intersecting sets of spaced hyperbolic lines representative of different constant pulse transit difference intervals which also have said difierent pairs of transmitting points as foci.

23. A transmission system for a combined pulse transit time and phase comparison system of position determination, comprising two transmitters for radiating signals at different frequencies and at spaced radiation points, transmitting means for radiating pulsed signals alternately at two still diflerent frequencies from at least one additional radiation point, means responsive to said pulsed signals for alternately modulating the signals radiated by said two transmitters with reference signal pulses, said radiated signals effectively producing standing waves in space characterized by two intersecting sets of spaced hyperbolic isophase lines having different pairs of said transmitting points as foci and also by two intersecting sets of spaced hyperbolic lines representative of difierent constant pulse transit difference intervals which also have said different pairs of transmitting points as foci, and means included in said system for establishing spacial coincidence between at least a portion of said hyperbolic isophase lines and a corresponding portion of the hyperbolic lines representative of different constant pulse transit difference intervals.

24. A transmission system for a combined pulse transit time and phase comparison system of position determination, comprising two transmitters for radiating signals at different frequencies and at spaced radiation points, transmitting means for radiating pulsed signals alternately at two still different frequencies from at least one additional radiation point, means responsive to said pulsed signals for alternately modulating the signals radiated by said two transmitters with reference signal pulses, said radiated signals effectively producing standing waves in space characterized by two intersecting sets of spaced hyperbolic isophase lines having different pairs of said transmitting points as foci and also by two intersecting sets of spaced hyperbolic lines representative of different constant pulse transit difference intervals which also have said different pairs of transmitting points as foci, and reference pulse transit time control means interposed in the paths of modulation of said two transmitters for establishing spacial coincidence between at least a portion of said hyperbolic isophase lines and a corresponding portion of the hyperbolic lines representative of different constant pulse transit difference intervals.

25. A transmission system for a combined pulse 28 transit time and phase comparison system of position determination, comprising spaced first and second transmitters for radiating signals of different frequencies, transmitting means for radiating pulsed signals alternately at two still different frequencies from a third radiation point, and means responsive to said pulsed signals for alternately modulating the signals radiated by said first and second transmitters with reference signal pulses, the signals radiated by said first and second transmitters and the pulsed signal of one frequency effectively producing standing signal patterns in space characterized by a first set of spaced hyperbolic isophase lines having said third radiation point and said first transmitter as foci and also a first set of spaced hyperbolic lines representative of different constant pulse transit difference intervals which have said third radiation point and said second transmitter as foci, and the signals radiated by said first and second transmitters and the pulsed signal of the other frequency effectively producing standing signal patterns in space characterized by a second set of spaced hyperbolic isophase lines having said third radiation point and said second transmitter as foci and also a second set of spaced hyperbolic lines representative of different constant pulse transit difference intervals which have said third radiation point and said first transmitter as foci.

26. A transmission system for a combined pulse transit time and phase comparison system of position determination, comprising spaced first and second transmitters for radiating signals of different frequencies, transmitting means for radiating pulsed signals alternately at two still different frequencies from a third radiation point, means responsive to said pulsed signals for alternately modulating the signals radiated by said first and second transmitters with referencesignal pulses, the signals radiated by said first and second transmitters and the pulsed signal of one frequency effectively producing standing signal patterns in space characterized by a first set of spaced hyperbolic isophase lines having said third radiation point and said first transmitter as foci and also a first set of spaced hyperbolic lines representative of different constant pulse transit difference intervals which have said third radiation point and said second transmitter as foci, and the signals radiated by said first and second transmitters and the pulsed signal of the other frequency efiectively producing standing signal patterns in space characterized by a second set of spaced hyperbolic isophase lines having said third radiation point and said second transmitter as foci and also a second set of spaced hyperbolic lines representative of different constant pulse transit difference intervals which have said third radiation point and said first transmitter as foci, means included in said system for establishing spacial coincidence between at least a portion of the hyperbolic isophase lines of said first set and a corresponding portion of the hyperbolic lines of said second set of lines representative of different constant pulse transit difference intervals, and additional means included in said system for establishing spacial coincidence between at least a portion of the hyperbolic isophase lines of said second set and a corresponding portion of the hyperbolic lines of said first set of lines representative of diiferent constant pulse transit difference intervals.v

27. A transmission system for a combined pulse transit time and phase comparison system of poition de ermination, comprising spaced first and 29 second transmitters for radiating signals of different frequencies, transmitting means for radiating pulsed signals alternately at two still different frequencies from a third radiation point, means responsive to said pulsed signals for alternately modulating the signals radiated by said first and second transmitters with reference signal pulses, the signals radiated by said first and second transmitters and the pulsed signal of one frequency effectively producing standing signal patterns in space characterized by a first set of spaced hyperbolic isophase lines having said third radiation point and said first transmitter as foci and also a first set of spaced hyperbolic lines representative of different constant pulse transit difference intervals which have said third radiation point and said second transmitter as foci, and the signals radiated by said first and second transmitters and the pulsed signal of the other frequency effectively producing standing signal patterns in space characterized by a second set of spaced hyperbolic isophase lines having said third radiation point and said second transmitter as foci and also a second set of spaced hyperbolic lines representativeof different constant pulse transit difference intervals which have said third radiation point and said first transmitter as foci, reference pulse transit time control means interposed in the path of reference pulse modulation of said first transmitter for establishing spacial coincidence between at least a portion of the hyperbolic isophase lines of said first set and a corresponding portion of the hyperbolic lines of said second set of lines representative of different constant pulse transit difference intervals, and

' additional reference pulse transit time control means interposed in the path of reference pulse modulation of said second transmitter for establsihing spacial coincidence between at least a portion of the hyperbolic isophase lines of said second set and a corresponding portion of the hyperbolic lines of said first set of lines representative of different constant pulse transit difference intervals.

28. A transmission system for a combined pulse transit time and phase comparison system of position determination, comprising spaced first'and second transmitters for radiating signals of different frequencies, transmitting means for radiating pulsed signals alternately at two still different frequencies from at least one additional radiation point, means for heterodyning one of said pulsed signals with the signal radiated by said second transmitter to develop a pulsed reference signal having a frequency related to the beat frequency of the heterodyned signals and for modulating said pulsed reference signal upon the signal radiated by said first transmitter, means for heterodyning the other of said pulsed signals with the signal radiated by said first transmitter to develop a second pulsed reference signal having a frequency related to the beat frequency of the heterodyned signals and for modulating said second pulsed reference signal upon the signal radiated by'said second transmitter, and means interposed in the paths of modulation of said transmitters for determining the time relationship between the signal pulses radiated by said transmitting means and the corresponding reference signal pulses radiated by said transmitters.

29. A transmission system for a combined pulse transit time and phase comparison system of position determination, comprising spaced first and second'transmitters for radiating signals of 30 different frequencies, transmitting mean for radiating pulsed signals alternately at two still different frequencies from a third radiation point, means for heterodyning one of said pulsed signals with the signal radiated by said second transmitter to develop a pulsed reference signal having a frequency related to the beat frequency of the heterodyned signals and for modulating said pulsed reference signal upon the signal radiated by said first transmitter, and means for heterodyning the other of said pulsed signals with the signal radiated by said first transmitter to develop a second pulsed reference signal having a frequency related to the beat frequency of the heterodyned signals and for modulating said second pulsed reference signal on the signal radiated by said second transmitter, said one pulsed signal and the signals radiated by said transmitters effectively producing standing signal patterns in space characterized by a first set of hyperbolic isophase lines having said first transmitter and said third radiation point as foci and also by a first set of spaced hyperbolic lines representative of different constant pulse transit difference intervals having said second transmitter and said third radiation point as foci, and said other pulsed signal and the signals radiated by said transmitters effectively producing standing signal patterns in space characterized by a second set of hyperbolic isophase lines having said second transmitter and said third radiation point as foci and also by a second set of spaced hyperbolic lines representative of different constant pulse transit difference intervals having said first transmitter and said third radiation point as foci.

30. A transmission system for a combined pulse transit time and phase comparison system of position determination, comprising spaced first and second transmitters for radiating signals of different frequencies, transmitting means for radiating pulsed signals alternately at two still different frequencies from a third radiation point, means for heterodyning one of said pulsed signals with the signal radiated by said second transmitter to develop a pulsed reference signal having a frequency related to the beat frequency of the heterodyned signals and for modulating said pulsed reference signal upon the signal radiated by said first transmitter, means for heterodyning the other of said pulsed signals with the signal radiated by'said first transmitter to develop a second pulsed reference signal having a frequency related to the beat frequency of the heterodyned signals and for modulating said second pulsed reference signal on the signal radiated by said second transmitter, said one pulsed signal and the signals radiated by said transmitters effectively producing standing signal patterns in space characterized by a first set of hyperbolic isophase line" having said first transmitter and said third radiation point as foci and also by a first set of spaced hyperbolic lines representative of different constant pulse transit difference intervals having said second transmitter and said third radiation point as foci, and said other pulsed signal and the signals radiated by said transmitters effectively producing standing signal patterns in space characterized by a second set of hyperbolic isophase lines having said second transmitter and sad third radiation point as foci and also by a second set of spaced hyperbolic lines representative of different constant pulse transit difference intervals having said first transmitter and said third radiation point as foci, and means included in said system for establishing spacial coincidence 31 between at least portions of the hyperbolic isophase lines of said first and second sets and corresponding portions of said second and first sets, respectively, of hyperbolic lines representative of different constant pulse transit difference intervals.

31. A- transmission system for a combined pulse transit time and phase comparison system of position determination, comprising spaced first and second transmitters for radiating signals of different frequencies, transmitting means for radiating pulsed signals alternately at two still dlfierent frequencies from a third radiation point, means for heterodyning one of said pulsed signals with the signal radiated by said second transmitter to develop a pulsed reference signal having a frequency relatedvto the beat frequency of the heterodyned signals and for modulating said pulsed reference signal upon the signal radiated by said first transmitter, means for heterodyning the other of said pulsed signals with the signal radiated by said first transmitter to develop a second pulsed reference signal having a frequency related to the beat frequency of the heterodyned signals and for modulating said second pulsed reference signal on the signal radiated by said second transmitter, said one pulsed signal and the signals radiated by said transmitters effectively producing standing signal patterns in space characterized by a first set of hyperbolic isophase lines having said first transmitter and said third radiationspoint as foci and also by a first set of spaced hyperbolic lines representative of different constant pulse transit difference intervals having said second transmitter and said third radiation point as foci, and said other pulsed signal and the signals radiated by said transmitters effectively producing standing signal patterns in space characterized by a second set of hyperbolic isophase lines having said second transmitter and said third radiation point as tool and also by a second set of spaced hyperbolic lines representative of different constant pulse transit difference intervals having said first transmitter and said third radiation point as foci, reference pulse transit delay means interposed in the path of modulation of said first transmitter for establishing spacial coincidence between at least a portion of the hyperbolic isophase lines of said first set and a corresponding portion of the hyperbolic lines of the second set of lines representative of different constant pulse transit difierence intervals, and additional reference pulse transit delay means interposed in the path of modulation of said second transmitter for establishing spacial coincidence between at least a portion of the hyperbolic isophase lines of said second set and a corresponding portion of the hyperbolic lines of the first set of lines representative of different constant pulse transit difference intervals.

32. Wave signal receiving and translating apparatus for translating pulsed signals into position indications, comprising a pair of receivers for producing a pair of pulsed position indicating signals in response to the separate reception of a pair of signals which are pulsed in synchronism and are transmitted to said receivers over differennt routes, means responsive to the time displacement between corresponding pulses of said position indicating signals for producing one position indication, and phase measuring means responsive to the phase relationship of the waves within corresponding pulses of said position indicating signals for producing a second position indication.

33. Wave signal receiving and translating apparatus for translating into position indications a pair of signals which are pulsed in synchronism and are transmitted to said apparatus over different routes, comprising a pair of receivers for separately receiving said signals and for converting said signals into correspondingly pulsed position indicating signals, pulse transit time comparison means responsive to the time displacement between correspondingpulses of said position indicating signals for producing one position indication, and phase measuring means responsive to the phase relationship of the waves of said position indicating signals for producing a second position indication.

34. Wave signal receiving apparatus for translating into position indications two sets of three signals, at least two of the signals of each set being pulsed in synchronism and the pulsed signals of the two sets being alternately pulsed, a first receiver for receiving a pair of signals of one of said sets of signals and for heterodyning the received signals to produce a first pulsed position indicating signal having a frequency related to the difference frequency of the heterodyned signals, a second receiver for receiving the third 5 nal of said one set of signals and for reproducing the pulses thereof to develop a second pulsed position indicating signal having the same frequency as said first pulsed position indicating signal, said second receiver being alternately operative to receive and heterodyne a pair of signals of the other of said sets of signals, thereby to produce a third pulsed position indicating signal having a frequency related to the difference frequency of the heterodyned signals, and said first receiver being concurrently operative to receive the third signal of said other set of signals and to reproduce the pulses thereof, thereby to develop a fourth pulsed position indicating signal having the same frequency as said third position indicating signal, pulse transit time comparison means alternately excited first b said first and second position indicating signals and then by said third and fourth position indicating signals and responsive to thetime displacement between corresponding pulses of the exciting signals for alternately producing two different position indications, and phase measuring means alternately excited first by said first and second position indicating signals and then by said third and fourth position indicating signals and responsive to the phase relationship of the waves within corresponding pulses of the exciting signals for alternately producing two additional position indications.

35. A pulse transit time system of position determination, comprising a first transmitter for continuously radiating a first signal of one frequency, a second transmitter for radiating a pulsed signal of difierent frequency, a third transmitter for radiating a carrier signal at a third frequency, heterodyning means for heterodyning said first and pulsed signals to produce a pulsed reference signal having a frequency related to the beat frequency between said first and pulsed signals, modulating means for modulating said pulsed reference signal upon the carrier signal radiated by said third transmitter, said signals effectively producing a standing signal pattern in space characterized by spaced hyperbolic lines representative of different constant pulse transit difference intervals which have the radiation points of said second and third transmitters as foci, means included in said system for determining the spacial disposition of at least certain of said hyperbolic lines, and a. receiving station including means responsiveto the pulsed signals radiated by said second and third transmitters for producing an indication representative of the position of said receiving station relative to certain of said lines.

36. A pulse transit time system of position determination, comprising a first transmitter for continuously radiating a first signal of one frequency, a second transmitter for radiating a pulsed signal of dlfierent frequency, a third transmitter for radiating a carrier signal at a third frequency, heterodyning means for heterodyning said first and pulsed signals to produce a pulsed reference signal having a frequency related to the beat frequency between said first and pulsed signals, modulating means for modulating said pulsed reference signal upon the carrier signal radiated by said third transmitter, said signals effectively producing a standing signal pattern in space characterized by spaced hyperbolic lines representative of different constant pulse transit difierence intervals which have the radiation points of said second and third transmitters as foci, reference pulse transit time delay means interposed between said heterodyning means and said modulating means to determine the spacial disposition of at least certain of said hyperbolic lines, and a receiving station including means re sponsive to the pulsed signals radiated by said second and third transmitters for producing an indication representative of the position of said receiving station relative to certain of said lines.

37. A pulse transit time system of position determination, comprising two transmitters for radiating signals at different frequencies and at spaced radiation points, transmitting means for radiating pulsed signals alternately at two still different frequencies from at least one additional radiation point, means responsive to said pulsed signals for alternately modulating the signals radiated by said two transmitters with reference signal pulses, said radiated signals effectively producing a standing signal pattern in space characterized by two intersecting sets of spaced hyperbolic lines representative of different constant pulse transit difference intervals which have different pairs of said transmitting points as foci, means included in said system for determining the spacial disposition of at least a portion of said hyperbolic lines, and a receiving station including pulse transit time comparison means re-' sponsive to said pulsed signals for producing indications representative of the position of said receiving station relative to certain of the lines in each of said sets of lines.

38. A pulse transit time system of position determination, comprising two transmitters for radiating signals at different frequencies and at spaced radiation points, transmitting means for radiating pulsed signals alternately at two still difierent frequencies from at least one additional radiation point, means responsive to said pulsed signals for alternately modulating the signals radiated by said two transmitters with reference signal pulses, said radiated signals effectively producing a standing signal pattern in space characterized by two intersecting sets of spaced hyperbolic lines representative of different constant pulse transit difference intervals which have difierent pairs of said transmitting points as foci. reference pulse transit time delay means interposed in the paths of modulation of said two transmitters for determining the spacial disposition of at least a portion of said hyperbolic lines, and a receiving station including pulse transit time comparison means responsive to said pulsed signals for producing indications representative of the position of said receiving station relative to certain'of the lines in each of saidsets of lines.

39. A transmission system for a pulse transit time system of position determination, comprising a pair of spaced transmitters for radiating signals of different frequencies, transmitting means for radiating pulsed signals alternately at two still different frequencies from at least one additional radiation point, means for heterodyning one of said pulsed, signals with the signal radiated by one of said transmitters to develop a pulsed reference signal and for modulating said pulse reference signal on the signal radiated by the other of said transmitters, means for heterodyning' the other of said pulsed signals with the signal radiated by the other of said transmitters to develop a second pulsed reference signal and for modulating said second pulsed reference signal on the signal radiated by said one transmitter, and means included in said system for determining the time relationship between the signal pulses radiated by said transmitting means and the corresponding reference signal pulses radiated by said transmitters.

40. A transmission system for a pulse transit time system of position determination, comprising a pair of spaced transmitters for radiating signals of diiferent frequencies, transmitting means for radiating pulsed signals alternately at two still difierent frequencies from at least one additional radiation point, means for heterodyning one of said pulsed signals with the signal radiated by one of said transmitters to develop a pulsed reference signal and for modulating said pulsed reference signal on the signal radiated by the other of said transmitters, means for heterodyning the other of said pulsed signals with the signal radiated by the other of said transmitters to develop a second pulsed reference signal and for modulating said second pulsed reference signal on the signal radiated by said one transmitter, and reference pulse transit delay means interposed in the paths of modulation of said transmitters for determining the time relationship between the signal pulses radiated by said transmitting means and the corresponding reference signal pulses radiated by said transmitters.

41. A transmission system for a pulse transit time system of position determination, comprising two transmitters for radiating signals at different frequencies and at spaced radiation points, transmitting means for radiating pulsed signals alternately at two still different frequencies from at least one additional radiation point, means responsive to said pulsed signals for alternately modulating the signals radiated by said two transmitters with reference signal pulses, and means included in said system for determining the time relationship between the signal pulses radiated by said transmitting means and the corresponding reference signal pulses radiated by said transmitters.

42. A transmission system for a pulse transit time system of position determination, comprising a first transmitter for continuously radiating a first signal of one frequency, a second transmitter for radiating a'pulsed signal of diiferent frequency, a third transmitter for radiating a carrier signal at a third frequency, heterodyning means for heterodyning said first and Pulsed 

